In optical fiber communications, it is often desirable and/or beneficial to monitor the health and status of an optical link, or optical pathway, for various purposes. For example, sometimes a link has to be analyzed to determine if a disconnect or fault in the optical pathway exists and/or where the fault is located.
Optical Time-Domain Reflectometry (OTDR) is one method used to locate such faults (e.g., a disconnect and/or break in the fiber) in fiber optic networks. In this method, a laser pulse is sent down a test fiber and reflected back by a fault in the optical pathway.
The reflected laser pulse is then received by a photodetector. The time period elapsed since the signal was sent indicates how far down the pathway the fault is located.
In order to test the optical pathway, the testing equipment can be connected via a fiber access point which adds components to the optical network and can degrade the signal as it travels along the optical pathway. Alternatively, in systems where optical pathways forming an optical network are constructed using a number of optical fibers, each forming a section of the pathway, an end of an optical fiber section can be located and disconnected from the optical network.
In such systems, each optical fiber section is attached to the end of another optical fiber section. In some embodiments, an end of one of the optical sections can be accessed and the testing apparatus can be connected thereto.
Such methods can result in periods where the fiber is out of the communications network and, therefore, can result in network downtime. However, the use of a separate testing apparatus to locate faults within an optical fiber can be time consuming and costly.
Current OTDR methods are not able to provide for the simultaneous transmission of data and OTDR pulses due to OTDR pulses interfering with data pulses, which can result in inaccurate detection by data receivers. One prior solution, which can be used in optical networks that employ wavelength division multiplexing (WDM) in order to avoid such interference, is to use separate wavelength channels for OTDR pulses and the data stream pulses. However, such methods may create inefficiencies by using an entire wavelength channel for OTDR pulses and thereby can reduce the ability for the channel to be used to transmit data.
Additionally, such OTDR methods may not adequately protect against and/or monitor security breaches (e.g., unauthorized “eavesdropping” by accessing a data stream). For instance, an unauthorized entity could avoid being detected by tapping only the wavelength channel or channels used for data transmission, while the channel used for OTDR pulses remains undisturbed.